Migration processes of co-doped Si and Be delta-planes in MBE-grown GaAs

The authors have used high depth-resolution SIMS profiling to investigate the broadening of delta-doped planes of Be and (Be+Si) in GaAs grown by molecular beam epitaxy. They have confirmed that concentration-dependent diffusion is the dominant broadening process for Be at growth temperatures <or=600 degrees C, and by incorporating Si atoms on the same plane, they have shown that this broadening can be completely inhibited. This suggests that the rapid diffusion process may be the result of mutual repulsion between the Be_Ga^- ions, and is prevented by the reverse field due to the Si_Ga⁺ ions, or by the formation of low-mobility Si_Ga⁺-Be_Ga^- complexes. The rapid diffusion of Si as Si_Ga-Si_As pairs is also reduced, and they believe this is a Fermi-level effect, the compensation by Be reducing the probability of Si_As formation. The surface segregation of Si is not affected, whereas that of Be is reduced, indicating that surface fields during growth contribute to this effect for Be, but not for Si.